1. Field of the Invention
The present invention relates to laser cladding methods where a powdered filler material is used and laser processing heads for laser cladding.
2. Description of the Related Art
In recent years, laser cladding in which a powdered filler material is used has been used for the direct production of near-net shape components and surface treatment techniques to impart functions such as abrasion resistance. In such laser cladding, the shape of a clad depends strongly on powder delivery. Therefore, various powder delivery methods, including controlling the direction of powder delivery with respect to the cladding direction (laser scanning direction) and increasing the stability of the powder feed rate, have been tried to achieve high-precision clad forming.
For example, JP-A Hei 2 (1990)-258186 (U.S. Pat. No. 307,796) discloses a method for controlling the position where powder flow concentrates most (hereinafter referred to as “powder concentration position”) with respect to the laser optical axis. In this method, powder is delivered to a laser irradiation portion or in its proximity such that powder concentrates toward the laser optical axis from the periphery of the laser, and the powder concentration position is vertically adjustable along the laser optical axis. The laser cladding device used in this method includes a laser emitting unit and a powder feed nozzle provided around the periphery of the laser emitting unit, allowing powder to flow through the gap formed by the laser emitting unit and the powder feed nozzle. The powder concentration position is adjustable by vertically adjusting the relative position between the lower ends of the laser emitting unit and the powder feed nozzle to change the powder delivery angle.
In the laser cladding device described in JP-A Hei 2 (1990)-258186 (U.S. Pat. No. 307,796), adjusting the powder concentration position changes the diameter of the powder concentration position (hereinafter referred to as “powder concentration diameter”). Since adjusting one of the powder concentration position and the powder concentration diameter inevitably changes the other, in order to adjust both the powder concentration position and the powder concentration diameter at the same time, the positions of the laser emitting unit and the powder feed nozzle need to be adjusted vertically along the laser optical axis without changing the relative position between the lower ends of the laser emitting unit and the powder feed nozzle.
Therefore, every time the cladding track width is changed, the cladding operation has to be discontinued to adjust the powder concentration position and the powder concentration diameter. Moreover, every time the powder concentration position and the powder concentration diameter are adjusted, the distance between the tip of the laser emitting unit and the surface of a workpiece changes. Consequently, when a shield gas to protect a cladding portion from the atmosphere is allowed to flow from the inside of the laser emitting unit, the shielding properties of the gas inevitably change every time the powder concentration position and the powder concentration diameter are adjusted. These factors conspire to impair the soundness of the laser cladding process (welding).